Clicking on a suggested command should insert the command into the editor.

Steps to reproduce:
1. create a new pjs program
2. type 'back'
3. click on 'background'

Expected behaviour: it should insert 'background'
Observed behaviour: it does nothing

Reproduce the issue in a new pjs program by typing 'back' and clicking the 'background' suggestion, then trace the editor's suggestion-click handling. Done means the selected suggestion inserts 'background' into the editor instead of doing nothing; verify the behavior with the reproduction steps.

Written by the indexing model from the issue text.